Fuel cell power plants with closed water circulating systems are known in the prior art. It is highly preferably to operate these types of plants without requiring water, so called "make up" water, to be added to the system periodically. Since the electrochemical reaction in the power plant produces water as a by-product, this product water can be recovered and used to replenish water used by the power plant. The water in the circulating system is used for cooling the fuel cell and as steam in the fuel reforming process. To operate the plant, a raw hydrocarbon fuel such as methane, naphtha or the like is mixed with steam from the plant and catalytically reformed to a hydrogen rich fuel suitable for consumption in the power section. Depending on the nitrogen content of the raw hydrocarbon fuel, the reformed fuel gas will contain varying amounts of ammonia, as well as other noncondensable gases such as carbon dioxide, carbon monoxide and argon. The amount of ammonia in the fuel gas can be as high as 550 ppm by volume, and, since ammonia is harmful to the cells in the power section, it must be reduced to less than 2 ppm by volume before the fuel gas is fed into the power section. The decontamination of the fuel gas is accomplished in a vessel called a "contact cooler". The fuel gas is fed from the reformer into the bottom of the contact cooler wherein it then rises in the contact cooler vessel. At the top of the contact cooler, cool water is sprayed into the rising flow of fuel gas. The cool water both lowers the temperature of the fuel gas to a level suitable for use in the power section, and also strips out the ammonia, some carbon dioxide, carbon monoxide and argon, as well as some hydrogen, from the fuel gas. This operation also condenses the steam out of the fuel gas. The resultant contaminated water then settles into a sump at the bottom of the contact cooler and is continuously withdrawn therefrom. This water must be cleansed of the ammonia, carbon dioxide, carbon monoxide, argon and hydrogen contaminants before it can be reused in the power plant. The water could readily be decontaminated with conventional ion exchange demineralizing beds of the type used in fuel cell power plants. The use of the standard on-board demineralizing beds is not acceptable, however, with power plants having closed water circulation systems because the demineralizing beds, when used to decontaminate the water directly from the contact cooler, must be frequently regenerated. During regeneration of the ion exchange beds, waste water is created in the power plant which must be removed. This means that excessive make up water must be employed when the demineralizing beds are used to decontaminate the contact cooler drain water. It is thus apparent that this solution is not satisfactory for a power plant with a closed water circulating system which relies solely on the recovery of product water for replenishing water used during operation of the power plant.
The amount of ammonia contained in the water from the contact cooler will be about 400 ppm by weight or less. While this is a relatively small amount, it still affects the power plant adversely and must be lowered to about 30 ppm by weight or less. Once the ammonia concentrations are lowered to the 30 ppm by weight level, the water can be further stripped of ammonia in the on-board demineralizing beds without harming the latter. The chemical equivalents ratio of the ammonia to carbon dioxide in the contaminated water is about one to one. When ammonia alone is present as a contaminant in the water, one way of removing the ammonia has been to strip it from the water with steam. The steam will be passed through the water and will entrain the ammonia in a gaseous form, thereby removing the ammonia from the water. When the ammonia is present along with an acid gas such as carbon dioxide, problems are seen to arise when one tries to strip the ammonia and carbon dioxide from the water with steam alone, as noted in U.S. Pat. Nos. 3,754,376 granted Aug. 28, 1973 to R. D. Kent; and 4,547,293 granted Oct. 15, 1985 to C. J. King et al. The prior art indicates generally that the ammonia and carbonates can not be steam stripped in a single procedure, but must be stripped in separate steps at different controlled pH values, with the carbonate stripping out at a lower pH and the ammonia stripping out at a higher pH. Certain art, as exemplified by East German Patent No. 76,213 of Sept. 20, 1970, discloses that ammonia and carbonate ions will form unstable compounds in liquors produced in the soda industries, which compounds can be steam stripped from the liquors when the ammonia content of the liquors is very high, as for example, above 150,000 ppm levels. When the ammonia content is present at lower levels, however, as for example, about 18,000 ppm by volume, the two stage separation approach is seen to be necessary, as set forth in U.S. Pat. No. 4,352,680 granted Oct. 5, 1982 to E. Hackler.
Since the addition of chemicals to adjust the pH of the water could increase the total dissolved contaminants in the water, the subsequent burden on the fuel cell power plant demineralizing beds and their waste water quantities could exceed that due to the ammonia and carbon dioxide problem. This is unacceptable to fuel cell power plants with closed water systems.